The present invention relates to electro-mechanical systems for inspecting the insides of buried pipes and other conduits for defects and obstructions, and more particularly, to a video camera head having thermal feedback control of its lighting in order to reduce unwanted noise in the video output signal, avoid burning a user""s fingers and prevent damage to its electronic compnents.
There are many situations where it is desirable to internally inspect long lengths of pipe which are already in place, either underground, in a building, or underwater. For example, sewer and drain pipes frequently need to be internally inspected to diagnose existing problems or to determine if there are any breaks causing leakage or obstructions impairing the free flow of waste. It is also important to internally inspect steam pipes, heat exchanger pipes, water pipes, gas pipes, electrical conduits and fiber optic conduits. Frequently, pipes which are to be internally inspected have an internal diameter of six inches or less. It is sometimes necessary to inspect several hundred feet of pipe.
Over the years, video pipe inspection systems have been developed which typically include a camera which is forced down the pipe so that its interior can be viewed on a video display. It is common to record the inspection on a video recorder (xe2x80x9cVCRxe2x80x9d). Conventional video pipe inspection systems include a push cable which provides an electro-mechanical connection between a rugged head enclosing and protecting the video camera and a rotatable push reel which is used to pay out cable and force the head down the pipe. The push cable must be specially constructed in order to be flexible enough to make tight turns yet rigid enough to be pushed hundreds of feet down small diameter pipe. The push cable must also incorporate electrically conductive or fiber optic cable having the proper impedance for conveying the NTSC or other video signal to the video display unit and additional power and ground conductors.
Among other factors, the noise generated by the electronic circuitry of the video camera establishes the minimum luminescence or lighting required by camera to produce a clear high resolution color image. Heretofore it has been conventional to use light emitting diodes (xe2x80x9cLEDsxe2x80x9d) mounted in the distal end of the housing of the camera head to illuminate the interior or the pipe. In some cases as many as fifty or more LEDs are mounted in the camera head, each dissipating up to one hundred and sixty milliwatts (xe2x80x9cmWxe2x80x9d) of power. By way of example, in a conventional camera head the video camera itself may dissipate approximately one and one-half watts of power and the plurality of LEDs that provide the required lighting may dissipate eight watts of power. Due to the close physical proximity of the LEDs and the video camera, the excess heat generated by the LEDs inevitably produces high temperatures near the image sensing device of the video camera. The sensing device of the video camera is typically a charge coupled device (xe2x80x9cCCDxe2x80x9d). As the temperature of the CCD increases, the resulting noise induced in the video output signal increases, typically as the square root of the temperature increase of the CCD. A point of diminishing returns is reached where the thermal noise increases dramatically. When the CCD reaches a predetermined maximum operating temperature, e.g. one hundred and sixty degrees F., the resulting thermal noise induced in the video output signal becomes excessive. If the CCD is subjected to a temperature above its predetermined maximum operating temperature for too long, the performance of the video camera can be permanently degraded. The build-up of heat can become so excessive as to actually burn a user""s fingers when handling the camera head.
The ability of the camera head to dissipate heat depends not only upon its internal construction, but upon the nature of its environment, e.g. ambient temperature, humidity, whether it is surrounded by liquid or air, etc. It would therefore be desirable to provide a video camera head that could utilize maximum lighting without generating excessive heat.
The present invention provides a video camera head particularly adapted for pipe inspection having thermal feedback control of its lighting in order to lower its temperature and reduce unwanted noise in the video output signal. The camera head includes a camera housing having a hollow interior. A video camera is mounted inside the housing for generating video signals of an image of an interior of a pipe. The camera has an image sensing device with a predetermined maximum operating temperature. Mechanisms are provided for operatively coupling a video push cable to the camera housing and the video camera. At least one light emitting diode is mounted in the forward end of the housing for illuminating the interior of the pipe. A drive circuit is connected to the light emitting diode for driving the light emitting diode with a predetermined electrical drive signal. The drive circuit includes a feedback loop for controlling the level of power dissipated by the light emitting diode in order to ensure that the operating temperature of the image sensing device does not exceed the predetermined maximum operating temperature.
The present invention also provides a method of providing video images of the inside of a pipe. The method involves mounting a video camera inside a housing for generating video signals of an image of an interior of a pipe, the camera having an image sensing device with a predetermined maximum operating temperature. The method further involves operatively connecting the housing and the camera to the distal end of a video push cable and pushing the housing and video camera down the interior of the pipe by paying out the video push cable. The method further involves driving at least one light emitting diode mounted in a front end of the housing with a predetermined electrical drive signal to illuminate the interior of the pipe and controlling the level of power dissipated by the light emitting diode in order to ensure that the operating temperature of the image sensing device of the video camera does not exceed the predetermined maximum operating temperature. Finally, the method involves displaying images of the interior of the pipe generated from a video output signal conveyed from the video camera over the video push cable.